The present invention relates to cooling fins for dissipating heat from cooling fluid used with electrical transformers and other devices and more particularly to a liquid filled cooling fin with reinforcing ribs formed into the fin surfaces to increase the pressure withstand capability of the fin without requiring mechanical attachment of opposing fin walls over the cooling surfaces of the fin.
Electric transformers and other devices, which in the course of normal operation generate potentially harmful heat, are typically located within a tank filled with a cooling fluid in which the transformer is submerged and which transfers heat away from the transformer. To increase the heat dissipation from the tank, it may be provided with additional heat transfer surface, such as a radiator, heat exchanger, or cooling fins for transferring heat from the cooling fluid to ambient air. Cooling fins generally consist of two, roughly rectangular, opposing fin walls separated by a relatively thin liquid space. The walls are sealed together at both ends along the depth of the fin and at one of the two edges (the "nose" of the fin) along the height of the fin. The second, open edge of the fin, generally known as the fin "root" or base, is attached along the height of the fin in a liquid tight seal to the transformer tank. The tank is provided with holes or other fluid passages so that cooling fluid can circulate between the tank and the fin.
The cooling fins are liquid filled and may vary in size and structural configuration depending on the amount of heat produced by the transformer, the ambient temperature, and cooling fluid characteristics. Cooling fluid is heated in the tank by the transformer and flows from the tank to the cooling fins, where it is then cooled by transferring heat through the fin walls to ambient air. The cooled cooling fluid then circulates back to the tank, completing a circulation pattern which is continuously repeated in operation.
As the cooling fluid is heated, its pressure increases. The pressure inside the transformer tank and the cooling fins therefore increases as the cooling fluid temperature increases. It is thus important to transformer operability that the fins be capable of withstanding the cooling fluid pressure. For a given tank size, larger liquid filled fins are used to increase the heat dissipation. A deficiency of prior art fins is that as fin size increases, the cooling fluid pressure at which the fin deforms decreases. For example, It is known from practice and experimentation that plain wall liquid filled cooling fins 54 inches high and 10 inches deep begin to permanently deform at cooling fluid pressures between 7 psig and 10 psig. Thus it has been the case that fins larger than approximately 54 inches high and 10 inches deep cannot be successfully employed because they exhibit unacceptably high deformation at fluid pressures of approximately 7 psig. The pressure withstand capability of liquid filled cooling fins thus limits the maximum height and depth of a fin that can be used on a transformer tank.
A deficiency of prior art attempts to increase fin size and heat dissipation capacity is that such attempts have generally resulted in fins that are more complicated in design and construction in order to withstand the cooling fluid pressure. For example, fins including extensive troughs or dimples typically require a considerable number of spot welds between opposing fin walls, and are consequently more expensive to manufacture than plain wall fins.
The primary mode of fin deformation is by increase in the fin thickness, "ballooning" the opposing walls of the fin outward. The fin experiences two modes of failure from deformation due to pressure loading. The first mode is permanent deformation of the fin walls such that the fin walls do not return to their originally manufactured shape and size after removal of the pressure load. The second mode is catastrophic failure, in which the fin deforms sufficiently to cause excess loading of welded connections and weld failure, typically at the ends of the fin. A liquid filled cooling fin which could be increased in size while maintaining satisfactory pressure withstand capability would therefore be welcomed in the field.
Attempts to overcome the deficiencies of prior art fins have included mechanical fastening of the two opposing fin walls at locations between the fin ends and between the fin nose and root. For example, U.S. Pat. No. 4,413,674 discloses reinforcing the fin panel by spot welding the opposing walls of the fin together in the presence of formed dimples or troughs. This mechanical fastening requires matching indentations in the opposing fin walls that are to be fastened together. Mechanically fastened fins are more costly, more difficult to form and manufacture, and can result in the formation of weak points and leaks in the fin walls. Further, fabricating extensive troughs or dimples in the fin wall can distort the fin, leading to a poor fit to the transformer tank.
The pressure withstand capability of large fins may also be increased by manufacturing fins of heavier gage or higher strength materials. These approaches result in higher material costs as well as higher fabrication costs. The present invention overcomes the deficiencies of the prior art.